F1 Seedlings Research Articles

Intraspecific hybridization of low chill peach cultivars for superior fruit quality and their hybridity confirmation by SSR markers

The present investigation was carried out to develop of low chill peach hybrids for superior fruit quality during the year 2016 and 2017. Crosses were made between low chill peach cultivars, taking Flordaglo and Florda Crest as a female parent and Florda Prince, Florda Grand, Florda Crest and Yumyoeng as male parents. Among the hybrids, the maximum fruit set (59.28%) was observed in H3, while the minimum fruit set (38.56%) was recorded in H6. Among the parents crossed, the maximum fruit set (82.32%) and fruit retention (53.23%) was observed in Florda Prince while the minimum fruit set (56.42%) and fruit retention (33.56%) was noticed in Yumyoeng. In the low chill hybrids developed, fruit retention percent was recorded the maximum (74.50%) and the minimum (41.27%) in H1 and H4. Crosses of Florda Crest as female noticed the maximum fruit drop percentage with H5 having highest (74.61%) fruit drop percentage while hybrid H1 observed the minimum (25.84%) fruit drop percentage. Among the parents, Yumyoeng showed maximum (53.79%) while Florda Crest showed minimum (43.94%) fruit drop percentage. Seeds of hybrid H6 took the maximum days for stratification (77 days) while H2 took the minimum days for stratification (69 days). The minimum (10.30 days) and the maximum (15.58 days) number of days taken for seed germination was noticed in H3 and H5, respectively. After sowing the seeds in the protrays, H1 observed the maximum seed germination percentage (90.41%) while minimum (43.38%) percent of seed germination was recorded in H6. A significant variation was recorded between the traits viz., seedling height, intermodal length and rosetting percentage among different peach hybrids. Among the 22 SSR markers, only six markers (MA015a, MA020a, MA023a, CPPCT-022, CPPCT-030 and UDP96–005) were found to be able to test the hybridity of F1 seedling.

A New Resistance Gene in Combination with Rmg8 Confers Strong Resistance Against Triticum Isolates of Pyricularia oryzae in a Common Wheat Landrace.

The wheat blast fungus (Triticum pathotype of Pyricularia oryzae) first arose in Brazil in 1985 and has recently spread to Asia. Resistance genes against this new pathogen are very rare in common wheat populations. We screened 520 local landraces of common wheat collected worldwide with Br48, a Triticum isolate collected in Brazil, and found a highly resistant, unique accession, GR119. When F2 seedlings derived from a cross between GR119 and Chinese Spring (CS, susceptible control) were inoculated with Br48, resistant and susceptible seedlings segregated in a 15:1 ratio, suggesting that GR119 carries two resistance genes. When the F2 seedlings were inoculated with Br48ΔA8 carrying a disrupted allele of AVR-Rmg8 (an avirulence gene corresponding to a previously reported resistance gene, Rmg8), however, the segregation fitted a 3:1 ratio. These results suggest that one of the two genes in GR119 was Rmg8. The other, new gene was tentatively designated as RmgGR119. GR119 was highly resistant to all Triticum isolates tested. Spikes of GR119 were highly resistant to Br48, moderately resistant to Br48ΔA8 and a hybrid culture carrying avr-Rmg8 (nonfunctional allele), and highly resistant to its transformant carrying AVR-Rmg8. The strong resistance of GR119 was attributed to the combined effects of Rmg8 and RmgGR119.

Karyologic and Heterosis Studies of the Artificial Inter- and Intraspecific Hybrids of Viola ×wittrockiana and Viola cornuta

An artificial crossing was made between four Viola ×wittrockiana (2n = 48) lines and one Viola cornuta inbred (2n = 26) line as well as among V. ×wittrockiana lines to investigate the cytologic characteristics, fertility, and heteroses of hybrids. The sizes of flowers and stomata and the leaf areas of the V. ×wittrockiana plants were larger than those of the V. cornuta plants. The karyologic stability of V. cornuta was greater than that of V. ×wittrockiana, and ≈20% of individuals in the latter deviated from the given 2n = 48. Capsule setting after interspecies hand pollination ranged from 28% to 94%, and F1 seed germination ranged from 16% to 88%, revealing no obvious pre- or postzygotic selection mechanisms. The chromosome numbers in V. ×wittrockiana × V. cornuta F1 seedlings varied (2n = 34–38), with about half the cells exhibiting the intermediate (2n = 36) value. These interspecific hybrids exhibited positive heterosis in flower size (range, 11% to 66%) and negative heterosis in plant height (range, –12% to –57%). Both of these traits are desirable in pansy breeding programs.

Morphological characterization and hybridity confirmation of low chill peach (Prunus persica) hybrids using SSR markers

A hybridization programme was conducted during 2015 and 2016 with the main objective to widen the varietal range of early ripening cultivars. Crosses were made between low chill peach [Prunus persica (L.) Batsch] cultivars, taking Shan-i-Punjab and Tropic Sweet as a female and crossed with Florda Prince, Flordaglo and Prabhat and crosses of Shan-i-Punjab x Florda Prince showed maximum fruit set (72.63%), whereas minimum fruit set was recorded in Tropic Sweet × Flordaglo (18.87%). Although in Tropic Sweet crosses, fruit set was lower but they showed significantly higher percentage of fruit retention and lower percentage of fruit drop than the crosses made with Shan-i-Punjab cultivar. After ripening seeds were extracted from the fruits and were kept at low temperature for stratification until the seeds showed radicle emergence. Crosses made between Tropic Sweet × Flordaglo took maximum days for stratification (88.33). After sowing in the field maximum percentage of seed germination 90.43% was recorded in Tropic Sweet × Florda Prince seeds and maximum seedling height in Tropic Sweet × Flordaglo (36.03 cm). Very less variations were recorded among different crosses for petiole length and intermodal length and more rosetting was observed in Tropic Sweet hybrids. Among 22 SSR markers only six markers (MA015a, MA020a, MA023a, CPPCT-022, CPPCT-030 and UDP96-005) were able to test the hybridity of F1 seedling.

Effects of nitrogen loading under low and high phosphorus conditions on above- and below-ground growth of hybrid larch F1 seedlings

Under present environmental conditions, hybrid larch F1 (Larix gmelinii var. japonica × Larix kaempferi) is a promising afforestation species as it has a high growth rate and tolerance against grazing damage, disease and cold. However, the input of nitrogen (N) to forests due to the increase of anthropogenic N is causing imbalances of N compared to other nutrients, especially phosphorus (P), thus affecting the root growth of healthy seedlings. However, knowledge on how different N and P conditions affect F1 root growth is still limited. In this study, various N (3 levels) and P (no addition and addition) conditions were imposed to investigate the effect of N loading on larch F1 seedlings under different P conditions. Needle N: P ratio, aboveground growth, belowground growth as well as fine root production were measured. The results showed that needle N: P ratio was higher under low P loading, and aboveground growth of seedlings increased with N loading at both low and high P conditions. Relative fine root production was decreased by N loading. On the other hand, fine root to total dry proportion was increased by N loading at no P addition, suggesting that limited P availability could increase fine root production. Total root proportion to total dry mass was decreased by N loading at both P conditions. We concluded that N loading has different effects on above- and below-ground growth of larch F1 and its effects may also differ according to P conditions, indicating that both N and P conditions should be carefully considered when planting hybrid larch F1.

The investigation of pellicle peelability on Japanese chestnut cultivar of ‘Yakko’ ( Castanea crenata Sieb. et Zucc.)

Abstract Japanese chestnuts (Castanea crenata Sieb. et Zucc.) generally have difficult-peeling pellicles even after heating, making easy-peeling pellicle (EPP) an important breeding target. Recently, EPP cultivars ‘Porotan’ and ‘Porosuke’ were released by a government-funded breeding program. However, very few genotypes carry the major recessive gene responsible for the EPP trait, resulting in inbreeding within a narrow gene pool. To discover other genetic materials having the potential for EPP breeding, we evaluated the pellicle peelability of 59 accessions (51 Japanese local cultivars and 8 wild individuals) by using the high-temperature oil peeling method. We discovered that ‘Yakko’ had an exceptionally high pellicle peelability score (87%), close to that of ‘Porotan’ (94%). The results of segregation ratio analysis of pellicle peelability and genotype prediction by simple sequence repeat (SSR) markers among F1 seedlings suggested that the EPP alleles of ‘Porotan’ and ‘Yakko’ are at the same locus. However, a haplotype structure analysis of the EPP genome region with SSR markers revealed that both haplotypes of ‘Yakko’ differed from those of ‘Porotan’, suggesting that the EPP gene of ‘Yakko’ had a different origin from that of ‘Porotan’ or was inherited from a common ancestor many generations ago.

Genetic inheritance of pulp colour and selected traits of cassava (Manihot esculenta Crantz) at early generation selection.

The early generation selection of cassava quantitative and qualitative traits saves breeding resources as it can shorten breeding schemes. Inheritance analysis provides important breeding information for developing new improved varieties. This study aimed at developing an F1 segregating cassava population and determining mode of gene action of pulp colour and selected traits at early generation selection (F1 seedling and clones). The 15 families exhibited significant (P < 0.05) phenotypic variation between offspring. The general combining ability (GCA) was significant for all traits except cassava brown streak disease on leaves, whereas specific combining ability (SCA) was significant for all evaluated traits. The Garukansubire and Gitamisi genotypes were the best general combiners for improving fresh storage root yield, while G1 and G2 were the best general combiners for improved carotenoid (yellow/orange pulp colour) and delayed physiological postharvest deterioration. The pulp colour had the highest GCA/SCA ratio and percent sum of squares due to GCA. The 15 F1 families exhibited essential genetic diversity for cassava improvement. The expression of most cassava traits was controlled by both additive and non-additive gene action. The study elucidated the role of dominance effects over the additive effects for the evaluated traits. However, the pulp colour was predominantly controlled by additive gene action. This implies the possibility of improving cassava through conventional breeding using recurrent selection for most traits. © 2017 Society of Chemical Industry.

Variability and heredity of some qualitative and quantitative grapevine characteristics

Variability and mode of heredity of some important qualitative and quantitative grapevine characteristics in 45 seedlings of F1 generation obtained from crossing combination Seedling 113 x Muscat Hamburg were investigated in this study. The seedlings of F1 generation for the investigated characteristics were arranged in certain number of categories by the OIV method. As variability indexes, standard deviation (S) and coefficient of variation (V) were used. Evaluation of the mode of heredity was done by ?2 test and t-test. Considering examined characteristics, the highest variability showed grape yield (V=58.9%), and the lowest sugar content in must (V=16.3%). Color of berry skin, cluster resistance to Botrytis cinerea and leaf resistance to Plasmopara viticola showed monogenic mode of heredity. Exception from the monogenic mode of heredity was determined for the flavor of berry. Grape yield, bunch weight and berry weight showed negative heterosis. For the sugar content in must, domination of the parent with low sugar content in must was determined.

Identification of the resistance gene to powdery mildew in Chinese wheat landrace Baiyouyantiao

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most damaging diseases to wheat in the world. The cultivation of resistant varieties of wheat is essential for controlling the powdery mildew epidemic. Wheat landraces are important resources of resistance to many diseases. Mapping powdery mildew resistance genes from wheat landraces will promote the development of new varieties with disease resistance. The Chinese wheat landrace Baiyouyantiao possesses characteristic of disease resistance to powdery mildew. To identify the resistance gene in this landrace, Baiyouyantiao was crossed with the susceptible cultivar Jingshuang 16 and seedlings of parents and F1, BC1, F2, and F2:3 were tested with Bgt isolate E09. The genetic results showed that the resistance of Baiyouyantiao to E09 was controlled by a single recessive gene, tentatively designated PmBYYT. An Illumina wheat 90K single-nucleotide polymorphism (SNP) array was applied to screen polymorphisms between F2-resistant and F2-susceptible DNA bulks for identifying the chromosomal location of PmBYYT. A high percentage of polymorphic SNPs between the resistant and susceptible DNA bulks was found on chromosome 7B, indicating that PmBYYT may be located on this chromosome. A genetic linkage map of PmBYYT consisting of two simple sequence repeat markers and eight SNP markers was developed. The two flanking markers were SNP markers W7BL-8 and W7BL-15, with genetic distances of 3 and 2.9 cM, respectively. The results of this study demonstrated the rapid characterization of a wheat disease resistance gene and SNP marker development using the 90K SNP assay. The flanking markers of gene PmBYYT will benefit marker-assisted selection (MAS) and map-based cloning in breeding wheat cultivars with powdery mildew resistance.

Investigating long-term effect of nanoparticles on growth of Raphanus sativus plants: a trans-generational study.

In the past decade, there has been an unprecedented growth in the application of nanoparticles (NPs) worldwide. Even though the acute toxicity of CuO and ZnO NPs to plants has been investigated in past, the trans-generational effects of these NPs in the environment are still unknown. In this study, we investigated whether the treatment of radish plants with CuO and ZnO NPs as single compound and as a binary mixture (10, 100 and 1000 mg/Kg soil) through their lifecycle would affect the seed quality and the development of second-generation seedlings or not. Results showed reduced root length, shoot length and biomass in F1 seedlings of NPs treated plants. The treated F1 seeds had smaller seed weight with accumulated Cu and Zn. The effect of toxic interaction between CuO and ZnO on plant growth was antagonistic in nature. Evaluation of the trans-generational impact is important to understand the long-term effect of NPs on the environment.

Persistence of Resistance Alleles 1781, 2041, and 2078 in the Absence of Herbicide Selection

Core Ideas This research investigated whether a fitness penalty exists for three known mutations (Leu‐1781, Asn‐2041, and Gly‐2078) in clethodim‐resistant rigid ryegrass populations under wheat competition. The results revealed that in the absence of herbicide selection, no fitness cost was associated with Leu‐1781 and Asn‐2041 alleles, but Gly‐2078 alleles increased in frequency. The absence of fitness penalties associated with these resistant alleles suggests their frequency will not decrease over time in the absence of clethodim use. In Australia, over‐reliance on clethodim has resulted in the evolution of clethodim resistance in rigid ryegrass (Lolium rigidum Gaudin) populations. Many of these resistant populations contain amino acid modifications in acetyl co‐enzyme A carboxylase (ACCase), the target‐site for this herbicide. This study was conducted to determine whether a fitness penalty exists for three known mutations (Leu‐1781, Asn‐2041, and Gly‐2078) in clethodim‐resistant populations in the absence of herbicide selection pressure and presence of crop competition. In 2014, F2 seedlings of three clethodim‐resistant rigid ryegrass populations were planted in wheat (Triticum aestivum L.) crop under two densities (100 and 200 plants m−2). Sequencing of all individuals of each rigid ryegrass population was done to establish the initial frequency of each allele (no mutation, Leu‐1781, Asn‐2041, and Gly‐2078). The F2 plants were allowed to set seed and seeds were collected at the end of the season. In 2015, seedlings established from seed collected in 2014 were grown, and the sequence of ACCase gene examined to determine the change in frequency of each resistant allele. The results showed that there was no significant change in the frequency of Leu‐1781, and Asn‐2041 alleles in rigid ryegrass populations over one generation in the absence of clethodim use. However, Gly‐2078 increase was identified in three populations, even under different competition levels. The absence of fitness penalties associated with these resistant alleles suggests that their frequency will not decrease over time in the absence of clethodim use.

Phenotypic and Comparative Transcriptome Analysis of Different Ploidy Plants in Dendrocalamus latiflorus Munro.

Elucidating the differences in gene expression profiles of plants with different ploidy levels and how they affect phenotypic traits is vital to allow genetic improvement of plants such as Ma bamboo (Dendrocalamus latiflorus Munro). We previously obtained triploid (2n = 3X = 36), hexaploid (2n = 6X = 72), and dodecaploid (2n = 12X = 144) Ma bamboo plants from embryogenic callus by anther culturing. Phenotypic differences between these plants appeared to be correlated with differences in ploidy. Here, we performed transcriptome profiling and sequencing of anther-regenerated plants and F1 seedlings of different ploidy levels using RNA-Seq technology. Pair-wise comparisons of the four resulting libraries revealed 8,396 differentially expressed genes. These differentially expressed genes were annotated, functionally classified, and partially validated. We found that the chromosome doubling led to substantially up- or down-regulation of genes that were involved in cell growth and differentiation; the polyploidy levels altered the anatomical, physiological and growth characteristics, such as leaf thickness, fusoid cell and stomatal size, shoot number, photosynthesis and respiration rate and so on. Additionally, two candidate genes, EXPB3 and TCP with potenitial regulatory roles in cell division and differentiation, were identified through gene coexpresseion network analysis. These results highlight the significance of potential applications of polyploidy, and provide valuable information for the genetic breeding of bamboo species.

Construction of a genetic linkage map based on RAPD, AFLP, and SSR markers for tea plant (Camellia sinensis)

Based on double pseudo-testcross theory, a population of 79 F1 clones, which was derived from a crossing of two tea cultivars using a Japanese tea cultivar “Fushun” (Camellia sinensis) as female parent and a Korean tea cultivar “Kemsull” (C. sinensis) as male parent, was applied to construct a genetic linkage map with different molecular markers. Previously, 143 random amplified polymorphism DNA (RAPD) markers and 11 simple sequence repeat (SSR) loci developed from 41 decamer random primers and 60 published SSR primer pairs, respectively, were used into our mapping analysis. In the study of amplified fragment length polymorphism (AFLP), 2439 bands were generated from 27 primer combinations with an average number of 90.3 bands for each, of which 495 (20.3%) were polymorphic. The majority of those polymorphic markers segregated in accordance with Mendelian segregation ratios at p < 0.01 for 400 (80.8%) or at p < 0.05 for 382 (77.2%), of which 136 (34.0%) or 131 (34.3%) were at 3:1 segregation ratios and 264 (66.0%) or 251 (65.7%) were at 1:1 segregation ratios at p < 0.01 and p < 0.05, respectively. For developing more SSR markers, the transcriptome sequences of flowers and leaves of two parents were obtained using high throughput RNA sequencing and compared. Afterwards, 1800 potential polymorphic SSR markers were successfully developed and 296 of them were selected and experimentally validated with a subset of tea plants (including two parents and six F1 offspring), from which 75 (25.3%) were repeatably amplified and polymorphic between two parents. From that, 29 (38.7%) newly mined SSR markers were heterozygous in “Fushun” and/or “Kemsull” and showed segregant genotypes in F1 seedlings and were adoptable by JoinMap 4.0. Totally, 678 markers including 143 RAPDs, 11 public SSRs, 495 AFLPs, and 29 newly mined SSRs were conjointly used to construct a combined linkage map for tea plant. The new genetic map located 79 RAPDs, 5 public SSRs, 214 AFLPs, and 11 new SSRs developed from RNA seq technique and covered 1441.6 cM with an average distance of 4.7 cM between two adjacent markers. This map will lay a foundation for qualitative or quantitative trait loci (QTLs) analysis of important agronomic traits for tea plant in the future study.

Optimizing Resource Allocation in a Genomic Breeding Program for Perennial Ryegrass to Balance Genetic Gain, Cost, and Inbreeding

Genomic selection (GS) has been recognized as offering numerous potential benefits for ryegrass (Lolium perenne L.) breeding. While the theoretical benefits of GS in ryegrass breeding are clear, the best way to apply GS in practical breeding programs remains to be determined. The present study aimed to investigate genomic breeding options that best balance genetic gain, breeding costs, and the level of inbreeding using stochastic simulation. Nine GS scenarios were tested, including different numbers of selection candidates (10,000, 5000, and 2000 F1 seedlings) and three reference population sizes for GS composed of plots representing a sward‐based trial (500, 200, and 100 plots). Low to moderate prediction accuracy was achieved for productivity traits across cycles (i.e., 0.1–0.45 for yield [h2 = 0.3]). Scenarios with larger reference populations (i.e., 500 plots) achieved higher prediction accuracy but, when considering field trial costs, were more expensive per unit of genetic gain. All nine GS scenarios delivered significantly higher genetic gain (up to fourfold) than the conventional breeding scenario over a 20‐yr period. Scenarios with moderate selection intensity on F1 seedlings with fewer plots tested in field gave the most genetic gain per dollar invested (i.e., 2000 or 5000 F1 seedlings and 100 plots). However, all GS scenarios reduced genetic diversity in the breeding population more than phenotypic selection, highlighting the need to mitigate inbreeding when applying GS in perennial ryegrass.

Molecular identification of variety purity in a cotton hybrid with unknown parentage using DNA-SSR markers.

Molecular identification of hybrid purity is difficult in regional trials of cotton varieties and hybrid trials. In particular, the molecular detection of hybrid purity has not yet been reported in the case of unknown parentage. In this study, we screened 5000 pairs of primers and chose 17 pairs of core simple sequence repeat (SSR) primers to determine the F1 purity of Han6402. The results showed that the purity based on SSR markers reached 100%. Twelve of the 17 pairs of primers exhibited co-dominant banding patterns, and 5 showed non-co-dominant banding patterns. Moreover, we constructed an F1 SSR fingerprinting profile that enabled the identification of the authenticity of Han 6402. Using these primers, we subsequently detected 44 individual F2 seedlings, and the results exhibited different extents of separation, in which the majority of genotypes were heterozygous with co-dominance at most of the loci that differed from each other. The results validated the underlying heterozygous status of the F2 population at the molecular level. Therefore, we conclude that the set of core SSR primers can be used for the laboratory identification of the authenticity and purity of cotton hybrids, not only for distinguishing Fl hybrids or segregating F2 populations, but also for detecting volunteer seeds as fake F1 hybrids in the cotton hybrid industry, based on the hybrid fingerprinting.

Pertumbuhan Bibit F2 Jamur Tiram pada Berbagai Komposisi Media

Oyster mushroom (Pleurotus ostreatus) is one type of wood mushroom that is used as a vegetable and processed food. In the cultivation of oyster mushrooms (Pleurotus ostreatus), seeds are a determining factor. This study aims to obtain the best media composition in the growth of oyster mushroom F2 seedlings (Pleurotus ostreatus). The research conducted at the Amuntai STIPER Laboratory from April to June 2013, using a Completely Randomized Design (CRD), with 5 treatments and 4 replications. As a treatment, the composition of media (K) is (k1) 80% corn: 18% sawdust: 1% CaCO3: 1% CaSO4, (k2) 70% corn: 28% sawdust: 1% CaCO3: 1% CaSO4, ( k3) 60% corn: 38% sawdust: 1% CaCO3: 1% CaSO4, (k4) 50% corn: 48% sawdust: 1% CaCO3: 1% CaSO4, (k5) 40% corn: 58% sawdust : 1% CaCO3: 1% CaSO4. Observation data were analyzed by variance and DMRT follow-up at 5% level. The parameters observed were the growth of mycelium horizontally and vertically. The results showed that media composition (k2) 70% corn: 28% sawdust: 1% CaCO3: 1% CaSO4 gave the best results for F2 seedling growth

From America to the Holy Land: disentangling plant traits of the invasive Heterotheca subaxillaris (Lam.) Britton &amp; Rusby

Understanding which plant traits confer invasiveness has been a central question in biological invasions research. Heterotheca subaxillaris (camphor-weed), an American plant, is an important invader of coastal sand dunes in Israel. Nevertheless, there has been no comprehensive comparative analysis of H. subaxillaris plant traits from native versus introduced habitats that sheds light on the invasion success of this species in Israel. I studied H. subaxillaris from native (US) versus introduced (Israel) populations to identify functional traits that accorded this species invasion success in Israel. Plant traits considered were shoot and root biomass production, root–shoot ratio, shoot height, root length, number of inflorescences, achene number and mass, and life span. Achenes (seeds) of all populations were germinated under common growing conditions to produce F1 achenes. F1 seedlings were grown in a large-scale common garden aeroponic system until flowering and then harvested. Introduced populations exhibited marked differences in measured parameters than native populations. Notably, root length of introduced populations exceeded 5 m, almost fourfold greater than that of native populations, allowing access to soil moisture and nutrients from deep sand layers and late-summer flowering. Life span of introduced populations almost doubled that of American populations. To the best of my knowledge, this is the first documentation of adaptive micro-evolutionary change favoring deep root allocation and phenological change in an invasive species in sand dunes. Seemingly, a rapid evolutionary change favoring root resource allocation occurred within introduced populations, allowing establishment, expansion, and successful invasion in the harsh ecosystem of Israel’s coastal sand dunes.

Genetic mapping of resistance to the Ug99 race group of Puccinia graminis f. sp. tritici in a spring wheat landrace CItr 4311.

A gene for Ug99 resistance from wheat landrace CItr 4311 was detected on the long arm of chromosome 2B. Wheat landrace CItr 4311 has seedling resistance to stem rust caused by Puccinia graminis f. sp. tritici race TTKSK and field resistance to the Ug99 race group. Parents, F1 seedlings, 121 doubled haploid (DH) lines, and 124 recombinant inbred lines (RILs) developed from a cross between CItr 4311 and the susceptible line LMPG-6 were evaluated for seedling resistance to race TTKSK. Goodness-of-fit tests indicated that a single dominant gene in CItr 4311 conditioned the TTKSK resistance. The 90K wheat iSelect SNP platform was used to genotype parents and the DH population. The seedling resistance locus was mapped to the chromosome arm 2BL. Parents and the DH population were evaluated for field resistance in Kenya. One major QTL for the field resistance was consistently detected in the same region on 2BL as the seedling resistance. Using KASP assays, five linked SNP markers were used to verify the result in the 124 RIL, 35 wheat accessions, 46 DH lines from the LMPG-6/PI 165194 cross and F1 seedlings, and susceptible bulks derived from crosses between six resistant landraces with LMPG-6. Race specificity, mapping results, and haplotype similarity with lines with Sr9h (Gabo 56, Timstein, and PI 670015), support the hypothesis that the Sr gene in CItr 4311 and the landraces is Sr9h. The KASP assays developed in this study will be useful for pyramiding the TTKSK resistance from CItr 4311 with other Sr genes effective against Ug99.

Arabidopsis Myrosinase Genes AtTGG4 and AtTGG5 Are Root-Tip Specific and Contribute to Auxin Biosynthesis and Root-Growth Regulation.

Plant myrosinases (β-thioglucoside glucohydrolases) are classified into two subclasses, Myr I and Myr II. The biological function of Myr I has been characterized as a major biochemical defense against insect pests and pathogens in cruciferous plants. However, the biological function of Myr II remains obscure. We studied the function of two Myr II member genes AtTGG4 and AtTGG5 in Arabidopsis. RT-PCR showed that both genes were specifically expressed in roots. GUS-assay revealed that both genes were expressed in the root-tip but with difference: AtTGG4 was expressed in the elongation zone of the root-tip, while AtTGG5 was expressed in the whole root-tip. Moreover, myrosin cells that produce and store the Myr I myrosinases in aboveground organs were not observed in roots, and AtTGG4 and AtTGG5 were expressed in all cells of the specific region. A homozygous double mutant line tgg4tgg5 was obtained through cross-pollination between two T-DNA insertion lines, tgg4E8 and tgg5E12, by PCR-screening in the F2 and F3 generations. Analysis of myrosinase activity in roots of mutants revealed that AtTGG4 and AtTGG5 had additive effects and contributed 35% and 65% myrosinase activity in roots of the wild type Col-0, respectively, and myrosinase activity in tgg4tgg5 was severely repressed. When grown in Murashiege & Skoog (MS) medium or in soil with sufficient water, Col-0 had the shortest roots, and tgg4tgg5 had the longest roots, while tgg4E8 and tgg5E12 had intermediate root lengths. In contrast, when grown in soil with excessive water, Col-0 had the longest roots, and tgg4tgg5 had the shortest roots. These results suggested that AtTGG4 and AtTGG5 regulated root growth and had a role in flood tolerance. The auxin-indicator gene DR5::GUS was then introduced into tgg4tgg5 by cross-pollination. DR5::GUS expression patterns in seedlings of F1, F2, and F3 generations indicated that AtTGG4 and AtTGG5 contributed to auxin biosynthesis in roots. The proposed mechanism is that indolic glucosinolate is transported to the root-tip and converted to indole-3-acetonitrile (IAN) in the tryptophan-dependent pathways by AtTGG4 and AtTGG5, and IAN is finally converted to indole-3-acetic acid (IAA) by nitrilases in the root-tip. This mechanism guarantees the biosynthesis of IAA in correct cells of the root-tip and, thus, a correct auxin gradient is formed for healthy development of roots.

Genetic analysis and molecular mapping of a stripe rust resistance gene in wheat–Leymus mollis translocation line M8926-2

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most widespread and destructive diseases of wheat crop worldwide. Growing resistant cultivars is the preferred method of controlling diseases, but only a few effective genes are available. M8926-2, a translocation line developed from interspecific hybridization between Leymus mollis and a common wheat genotype 7182, is highly resistant to the prevalent Chinese Pst races. In order to identify gene(s) for stripe rust resistance, M8926-2 was crossed with susceptible genotype Mingxian 169, and seedlings of parents and F1, F2, and F2:3 progenies were tested with the most prevalent Pst race CYR32 under controlled greenhouse conditions. M8926-2 has a single dominant gene, designated as YrM8926, conferring all-stage resistance to CYR32. Genetic mapping was used to identify molecular markers linked to YrM8926. A linkage group of seven simple sequence repeat (SSR) markers was constructed for YrM8926 using 191 F2-2 population plants and the gene was located on wheat chromosome 2DS. The wheat-L. mollis translocation line background of M8926-2 and disease assessments indicated that YrM8926 is originally derived from L. mollis. The stripe rust resistance gene and closely linked molecular markers should be useful for pyramiding with other genes to develop wheat cultivars with high-level and long-term resistance to stripe rust.